In many clinical situations, blood vessels are occluded for a variety of purposes, such as to control bleeding, to prevent blood supply to tumors, and to block blood flow within an aneurysm, arteriovenous malformation, or arteriovenous fistula.
Embolization of blood vessels is particularly useful in treating aneurysms. Aneurysms are abnormal blood filled dilations of a blood vessel wall, which may rupture causing significant bleeding. For the cases of intracranial aneurysms, the significant bleeding may lead to damage to surrounding brain tissue or death. Intracranial aneurysms may be difficult to treat when they are formed in remote cerebral blood vessels, which are very difficult to access. If left untreated, hemodynamic forces of normal pulsatile blood flow can rupture fragile tissue in the area of the aneurysm causing a stroke.
Vaso-occlusive devices have been used in the treatment of aneurysms. Vaso-occlusive devices are surgical implants placed within blood vessels or vascular cavities, typically by using a catheter as a conduit, to arrest blood flow, form a thrombus and occlude the site. For instance, a stroke or other such vascular occurrence may be treated by placing a vaso-occlusive device proximal of the site to block the flow of blood to the site and alleviate the leakage. An aneurysm may similarly be treated by introducing one or more vaso-occlusive devices through the neck of the aneurysm. The placement of the vaso-occlusive device(s) helps cause a mass to form in the aneurismal sac and alleviate the potential for growth of the aneurysm and its subsequent rupture. Other diseases, such as tumors, may often be treated by occluding the blood flow to the tumor.
There are a variety of known vaso-occlusive devices suitable for creating an embolic obstruction for therapeutic purposes. One such device is found in U.S. Pat. No. 4,994,069, to Ritchart et al. That patent describes a vaso-occlusive coil that assumes a linear helical configuration when stretched and a folded convoluted configuration when relaxed. The coil has a stretched configuration when placed in a catheter, which is used in placement of the coil at the desired site, and assumes the convoluted configuration when the coil is ejected from the catheter and the coil relaxes. Ritchart et al. describes a variety of shapes, including “flower” shapes and double vortices. A random shape is described as well.
Vaso-occlusive coils having complex, three-dimensional structures in a relaxed configuration are described in U.S. Pat. No. 6,322,576B1 to Wallace et al. The coils may be deployed in the approximate shape of a sphere, an ovoid, a clover, a box-like structure or other distorted spherical shape. The patent also describes methods of winding the anatomically shaped vaso-occlusive device into appropriately shaped forms and annealing them to form various devices.
Vaso-occlusive coils having little or no inherent secondary shape have also been described. For instance, U.S. Pat. Nos. 5,690,666 and 5,826,587 both by Berenstein et al. describe coils having little or no shape after introduction into the vascular space.
In accordance with one aspect of the invention, a vaso-occlusive device having an internal active element with in-situ stiffening capability is provided. In one embodiment, the vaso-occlusive device includes a coil, with the active element disposed within a lumen of the coil. The active element can have any of a number of shapes, such as, by way of non-limiting examples, an elongate shape, a form of a sphere, a cone, a plate, a mesh, or some other customized shape. By way of a further non-limiting example, the active element can be made from an expansive material, such as a hydrogel, that causes the active element to expand when placed in a body. In such an embodiment, the expanded active element imparts a radial stress within the coil to thereby stiffen and stabilize at least a portion of the coil in-situ.
One problem associated with existing vaso-occlusive devices is that they may not have a sufficient strength or stiffness to retain their shape after they are delivered into an aneurysm. When the above-mentioned vaso-occlusive devices are placed within an aneurysm, they tend to induce a formation of a thrombi for occlusion of the aneurysm. However, with time and the influence of hemodynamic forces and thrombolytic processes, the delivered vaso-occlusive devices may move or change shape due to their relatively low stiffness or through the process of seeking a minimally energetic morphology. As a result, the delivered vaso-occlusive devices may move out of the position or shape in which they were originally placed. In some cases, the delivered vaso-occlusive devices may even dislodge out of the sack of an aneurysm.